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Abstract:

A device and method for gait training, such as for rehabilitation of a
person after a stroke is provided. In some embodiments, the device
comprises a stimulator, preferably electric stimulator, for provoking a
spinal cord withdrawal reflex in the person by stimulation on the
person's foot in response to a control signal. Hereby, the person's leg
will move and initiate a gait swing. A sensor is placed to sense movement
of the leg and provide a feedback signal accordingly. A processor unit
with a processor runs a control algorithm which calculates the control
signal in response to the feedback signal. Thus, the method is based on a
closed-loop design, and the control signal is preferably calculated for
each walking step, and it is preferably based on the feedback signal
obtained from the preceding walking step. Hereby reflex habituation can
be accounted for. Preferably, the stimulator has a plurality of
stimulator channels with electrodes placed on different sites distributed
on the sole of the foot and on the heel. The feedback signal may be based
on accelerometer(s), and/or gyroscope(s), and/or goinometer(s) positioned
on the leg and/or foot, e.g. partly or fully integrated in an in-sole for
a shoe etc.

Claims:

1. A device for gait training of a subject comprising: a stimulator
configured to generate a stimulation on a foot of the subject in response
to a control signal, wherein the stimulation is arranged to provoke a
spinal cord withdrawal reflex in the subject so as to cause the person's
leg to move, a sensor configured to sense a parameter representative of a
movement of the subject's leg and to generate a feedback signal
accordingly, and a processor unit operationally connected to the
stimulator and the sensor, the processor unit comprising a processor
running a control algorithm so as to generate the control signal in
response to the feedback signal.

2. The device according to claim 1, wherein the stimulator comprises an
electric stimulator configured to generate an electric stimulation on the
person's foot and thereby provoke the spinal cord reflex.

3. The device according to claim 1, wherein the control algorithm is
arranged to vary the control signal in response to the feedback signal so
as to optimize a quality of gait.

4. The device according to claim 1, wherein the stimulator comprises a
plurality of individually controllable stimulators spatially distributed
to provide stimulation on different positions on the subject's foot.

5. The device according to claim 4, wherein the stimulator comprises at
least a stimulator configured to stimulate the subject's heel and a
stimulator arranged to stimulate a position on the subject's sole of the
foot.

6. The device according to claim 5, wherein the stimulator comprises a
plurality of stimulator channels arranged to stimulate different sites on
the subject's foot.

7. The device according to claim 1, wherein the control algorithm and the
stimulator are arranged so as to vary at least one of: stimulation
intensity, stimulation duration, stimulation timing in the gait cycle, or
stimulation site in response to the feedback signal.

8. The device according to claim 7, wherein the control algorithm is
arranged to generate the control signal in response to the feedback
signal by selecting between one of a plurality of predetermined
stimulation options selected from the group consisting of stimulation
with different stimulation intensities, different stimulation timing in
the gait cycle, different stimulation duration, and different stimulation
sites.

9. The device according to claim 1, wherein the processor unit is
configured to calculate the control signal for each walking step of the
person.

10. The device according to claim 9, wherein the processor unit is
configured to calculate the control signal for a walking step based on
the feedback signal received during at least one previous walking step or
during the preceding walking step.

11. The device according to claim 10, wherein the control algorithm is
arranged to calculate an estimated deviation from a predetermined target
trajectory for a walking step based on the feedback signal from at least
one previous walking step.

12. The device according to claim 1, wherein the stimulator is configured
to generate a stimulation burst comprising a plurality of stimulations of
a stimulation duration of less than or equal to about 5 stimulations of a
stimulation duration of less than or equal to about 1 ms, with an
inter-stimulus interval of less than or equal to about 4 ms.

13. The device according to claim 12, wherein the stimulator is
configured to generate a stimulation sequence of 4 stimulation bursts.

14. The device according to claim 1, wherein the sensor comprises at
least one of: a sensor arranged to sense an angle of the subject's knee,
a sensor arranged to sense a distance between the subject's foot and the
ground below the foot, one or more contacts arranged to sense if the
subject's foot touches the ground, a sensor estimating an acceleration of
the leg, or a sensor estimating joint angle changes.

15. The device according to claim 1, wherein the stimulator is mounted in
a footwear, a sock, a shoe, or an in-sole for a shoe.

16. The device according to claim 15, wherein the sensor is mounted in
the form of a contact to sense if the foot touches the ground, in the
form of a laser device or ultrasonic device configured to measure a
distance between the foot and the ground, in the form of an
accelerometer, in the form of a gyroscope, or in the form of a tilt
sensor.

17. The device according to claim 1, wherein the processor unit is
implemented as a portable unit, which, optionally, may be attached to a
part of the subject's clothes.

18. The device according to claim 1, comprising a second stimulator
arranged for stimulation on the subject's opposite foot, and a second
sensor arranged to sense a second parameter representative of a position
of the subject's opposite leg, and, wherein the processor unit is
arranged to generate a second control signal to the second stimulator in
response to a second feedback signal from the second sensor, so as to
provoke movement of both legs of the subject.

19. A method of rehabilitation therapy of a gait impaired patient,
comprising: sensing a parameter representative of a position of the
patient's leg, and applying a simulation on the patient's foot in order
to provoke a spinal cord withdrawal reflex causing the patient's leg to
move, wherein the stimulation is determined in response to said parameter
representative of the position of the patient's leg.

20. A computer executable program code arranged to cause a computer
device to generate a control signal to a stimulator in response to a
feedback signal from a sensor so as to perform the method according to
claim 19.

Description:

FIELD OF THE INVENTION

[0001] The invention relates to the field of devices and methods for
functional therapy for patient suffering from a disorder causing gait
problems, such as patients suffering from stroke that inhibits or
eliminates the patient's gait ability. Especially, the invention relates
to functional electrical therapy.

BACKGROUND OF THE INVENTION

[0002] Patients that suffer from a gait disorder, e.g. patients being
partially or completely immobile due to a hemiparetic condition caused by
a stroke or traumatic brain injury, which has resulted in damage of an
area of their brain, have a significant better chance of rehabilitation
if intensive gait training is initiated within 3 months after the stroke.
In this early period, the brain is especially suited to
regenerate/relearn the ability to control the muscles, if the sufficient
sensory, learning input is provided, i.e. by completing functionally
adequate gait training. However, such gait training is often impossible
for the patient without help, if the brain area controlling the leg
muscles is completely damaged and thus unable to generate appropriate
motor control nerve signals in the normal way to make the patient walk.

[0003] The necessary electrical nerve signals to the leg muscles causing
the patient to walk can be synthesized by means of a computer or
processor that generates synthesized electric signals to each group of
muscles in the leg(s) in the right sequence via a large number of
implanted electrodes or cutaneously mounted electrodes. Such systems are
used for patients suffering from injuries in the spinal cord, i.e.
patients with a permanent interruption of nerve signals between the brain
and the legs. A less complex example of such synthesized gait aid is an
electronic device that helps patients suffering from the drop foot
syndrome.

[0004] However, for patients suffering from a stroke, the gait impairment
is often of a permanent character even though many patients manage to
walk by learning compensatory movements to move the paretic limb forward.
In particular lifting the leg by flexing the hip in the swing phase is
difficult. To relearn the gait function intense physiotherapy in the
sub-acute phase is critical. Electrical stimulation to support production
of the swing phase is suggested, which will allows extended daily
physiotherapy and more functional walking capability. For daily therapy
for in-patients stimulation of multiple muscles via several electrodes,
as used in existing devices or systems, are far too time consuming to
mount and take off in relation to daily physiotherapy. Moreover, direct
stimulation of hip flexor muscles are difficult due to the deep location
of these muscles.

SUMMARY OF THE INVENTION

[0005] Therefore, following the above description, there is a need for a
device and a method of therapy to help rehabilitation of patients
suffering from a stroke and thus temporarily needs assistance to be able
to perform gait training. The device should be easy to mount and take
off, in order to be efficient in practical therapy so as to utilize the
time spent by physiotherapeutic personal for the vital gait training of
the patient, and not for struggling with the equipment related to the
training.

[0006] In a first aspect, the invention provides a device arranged for
gait training, such as for rehabilitation of a person after a stroke, the
device comprising:

[0007] a stimulator arranged to generate a stimulation on the person's
foot in response to a control signal, wherein the stimulation is arranged
to provoke a spinal cord withdrawal reflex in the person so as to cause
the person's leg to move,

[0008] a sensor arranged to sense a parameter representative of a
movement, such as position, acceleration, velocity, of the person's leg
and to generate a feedback signal accordingly, and

[0009] a processor unit operationally connected to the stimulator and the
sensor, the processor unit comprising a processor running a control
algorithm so as to generate the control signal in response to the
feedback signal.

[0010] Such a device is highly suited for gait rehabilitation therapy of
post-stroke hemiparetic patients, since the person's own normally
functioning nociceptive withdrawal reflex (NWR) is triggered by
stimulation of the foot, thus causing the spinal cord to generate a
reflex in the form of integrated motor nerve signals leading to adequate
contraction of many muscles in the leg that make the person move his/her
leg upward and forward and thus initiate the swing phase during walking.
Even though this stereotyped flexion can be considered to provide an
uncontrollable leg movement, it has been shown in experiments that
suitable control of the stimulation, such as proper control us
stimulation site, stimulation intensity, stimulation timing, stimulation
duration, and stimulation frequency in response to the feedback signal it
is possible to evoke suitable hip, knee and ankle movement to allow a
functional gait cycle, which would otherwise be impossible for a
hemiparetic patient. Thus, the use of a closed-loop control system in the
generation of the electrical stimulation allows a quality of gait which
is acceptable for gait training. This approach enables sufficient
learning input to the brain to be able to regenerate its gait control
function and thus significantly improve the patient's chance of
completely restoring the patient's ability to walk and thus generally
increase the patient's quality of life.

[0011] With the closed loop configuration provided by the feedback signal,
e.g. representing an angle of the knee or another feedback parameter, the
control algorithm can be designed to optimize the gait by adjusting
different parameters of the stimulation, e.g. stimulus intensity or
stimulation site on the foot for each walking step and/or selection of
stimulation timing (phase of the gait cycle), such as selection of a
suitable stimulation of more stimulation sites versus time during the
gait cycle. Hereby, it is possible to avoid or at least suppress reflex
habituation effects and thus maintain a high quality of gait during
several walking steps and thereby follow a predetermined target
trajectory. Even though the rather powerful stimulation required is
perceived as painful, the patient has a positive experience with such
device, since the patient has the feeling of walking by their own effort
and a perception of rapid improvement of their walking performance. As
will be explained in more detail below, the required stimulation can be
implemented with only few units with rapid donning and doffing, and thus
save time that can be spent for the actual gait training. Hereby the
device is suited for physiotherapy clinics, hospitals or rehabilitation
centres etc.

[0012] In some embodiments, the stimulator comprises an electric
stimulator arranged to generate an electric stimulation on the person's
foot to provoke the spinal cord withdrawal reflex. In a preferred
embodiment, the stimulator can generate a sufficient electric current to
induce a withdrawal reaction via cutaneously applied electrodes on
multiple sites on the person's foot. Electric stimulation is
advantageous, since the intensity can rather easily be adjusted by
adjusting the applied current and stimulus duration. However, it is to be
understood that other types of stimulation on the foot can be used to
cause the withdrawal reflex.

[0013] The control algorithm may be arranged to vary the control signal in
response to the feedback signal so as to optimize gait quality, e.g. the
control algorithm may be arranged to optimize the gait by adjusting the
control signal and thus the stimulation so as to follow a target
trajectory for the gait. This may be in the form of knee angle versus
time during one walking step, in case the feedback from the sensor
includes a continuous representation of the knee angle of the person's
leg. Also, the precise stimulation timing during the step cycle can be
adjusted in response to the feedback signal in order to optimize gait
quality.

[0014] The stimulator preferably comprises a plurality of individually
controllable stimulation channels spatially distributed to provide
stimulation on different sites on the person's foot. Such plurality of
individually controllable channels may be in the form of spatially
distributed electric electrodes connected to individually controllable
control channels, either controllable via one common control signal or in
parallel control signals. The stimulator may especially comprise at least
a channel arranged to stimulate the posterior side of the heel and a
channel arranged to stimulate a position on the sole of the foot.
Especially, stimulation on the heel provokes a reflex in the form of a
forward movement of the leg which is critical for forward propulsion.
More specifically, the stimulator may comprise a plurality of stimulators
arranged to stimulate different positions on the person's foot. Moreover,
it is possible, for each walking step to switch to another stimulation
position and thereby avoid or at least suppress habituation to one
stimulation position. Furthermore, the quality of gait can be refined by
combining stimulation at several stimulation positions at the correct
timing during the step cycle. E.g. a heel stimulation to initiate the
swing followed by a stimulation of a distal part of the sole of the foot
so as to provoke an upward bending (dorsi flexion) of the foot.

[0015] The control algorithm and the stimulator are preferably arranged to
vary at least one of: stimulation intensity, stimulation duration, and
stimulation timing in response to the gait cycle measured by the feedback
signal. Most preferably, the control algorithm and stimulator are
arranged to vary more of these parameters in response to the feedback
signal at least stimulation duration and stimulation position on the
foot, so as to adapt stimulation to habituation effects, e.g. for
optimizing gait with respect to a target trajectory. The control
algorithm may be arranged to generate the control signal in response to
the feedback signal by selecting between one of a plurality of
predetermined stimulation options. Such plurality of stimulation options
may comprise stimulation options with different stimulation intensities,
different stimulation durations, and different stimulation positions
(sites). The selection between the predetermined options may be performed
between a number of predefined sets of stimulation parameters stored in
memory, and wherein each of said predefined sets of stimulation
parameters have been evaluated with respect to a target measure, thus
allowing a selection based on this target measure.

[0016] Preferably, to take into account habituation and gait quality, the
processor unit is arranged to calculate the control signal for each
walking step of the person. Preferably, the control signal for one
walking step is calculated based on the feedback signal received during
at least one previous walking step, such as during the preceding walking
step. More specifically, the control algorithm may be arranged to
calculate an estimated deviation from a predetermined target trajectory
for a walking step based on the feedback signal from at least one
previous walking step.

[0017] The stimulator may be arranged to generate a stimulation burst
comprising a plurality of stimulations of a stimulation duration, such as
less than or equal to about 5 stimulations of a stimulation duration of
less than or equal to about 1 ms with an inter-stimulus interval of less
than or equal to about 4 ms (e.g., less than or equal to about 5, 4, 3,
2, or 1 stimulation of a stimulation duration of less than or equal to
about 1, 0.75. 0.5, 0.25, or 0.1 ms with an inter-stimulus interval of
less than or equal to about 4, 3, 2, or 1 ms). Especially preferred
embodiments are configured such that the stimulator is arranged to
generate a stimulation sequence of a plurality of stimulation bursts,
such as a sequence of about 4 stimulation bursts. To adjust stimulation
intensity, it is possible to vary one or more of: current amplitude, the
number of stimulations in a burst, stimulation duration, inter-stimulus
interval, and the number of stimulations in one sequence. Some of such
sequences of stimulation bursts have been experimentally found to be
suitable.

[0018] The sensor may comprise at least one of: a sensor arranged to sense
an angle of the person's knee, a sensor arranged to sense a distance
between the person's foot and the ground below the foot, one or more
contacts arranged to sense if the person's foot touches the ground.
Preferably, the sensor is arranged to generate a continuous feedback
signal, or at least a sampled feedback signal allowing a sufficiently
precise tracking of the person's leg during one walking step. E.g. the
sensor may comprise two or more different types of separate sensors, so
as to allow a feedback signal with a more precise tracking of the gait.
E.g. the sensor may include an angular sensor to sense a knee angle, and
a contact under the foot to sense when the foot touches the ground. The
sensor may comprise one or more angular sensors to sense an angle of the
hip, knee, and ankle. Alternatively, or additionally, the sensor
comprises: an accelerometer positioned to sense a movement of the
person's foot or leg, a gyroscope arranged to sense a change in position
or angle of parts of the leg, e.g. joints, and a tilt sensor. One or more
of these sensor elements may be built into a sock or shoe so as to
eliminate the need for an individual mounting procedure.

[0019] In order to provide a therapy device with short donning/doffing
time, the stimulator or at least a part of the stimulator, e.g.
stimulator electrode(s), may be mounted in a footwear or part of the
footwear, such as a sock or an insole for a shoe, so as to facilitate
mounting of the stimulator on the person's foot. Especially, electric
electrodes may be mounted in a foot sole at different positions so as to
be able to electrically stimulate different positions on the foot, (e.g.
at least one heel position and 3, 4, or 5 positions distributed in a
length direction on the foot sole). The sensor may additionally or
alternatively be mounted in said footwear, such as in the form of a
contact to sense if the foot touches the ground, or in the form of a
laser device or ultrasonic device arranged to measure a distance between
the foot and the ground, and/or in the form of one or more
accelerometers.

[0020] The processor unit may be implemented as a portable unit, such as a
portable unit arranged for carrying by the person, such as arranged for
attachment to a part of the person clothes, e.g. adapted for mounting in
a person's belt.

[0021] To be suited for persons with both legs paralyzed, the device may
comprise a second stimulator arranged for stimulation on the person's
opposite foot, and a second sensor arranged to sense a second parameter
representative of a position of the person's opposite leg, and wherein
the processor unit is arranged to generate a second control signal to the
second stimulator in response to a second feedback signal from the second
sensor, so as to provoke movement of both legs of the person.

[0022] In a second aspect, the invention provides a method of
rehabilitation therapy of a gait impaired patient, such as a patient
suffering from a stroke, the method comprising:

[0023] sensing a parameter representative of a position of the person's
leg, and

[0024] applying a simulation on the person's foot in order to provoke a
spinal cord withdrawal reflex causing the person's leg to move, wherein
the stimulation is determined in response to said parameter
representative of the position of the person's leg.

[0025] In a third aspect, the invention provides a computer executable
program code arranged to cause a computer device to generate a control
signal to a stimulator in response to a feedback signal from a sensor so
as to perform the method according to the second aspect.

[0026] It is appreciated that the same advantages and equivalent
embodiments apply for the second and third aspects as mentioned for the
first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Embodiments of the invention will be described, by way of example
only, with reference to the drawings.

[0033]FIG. 8 illustrates the principles of a suitable control algorithm.

DETAILED DESCRIPTION

[0034] FIG. 1 shows schematically the leg LG and foot FT of a person
together with basic parts of a therapy device embodiment according to the
invention. The device includes a stimulator STM arranged to apply a
stimulation S on the foot FT with the purpose of provoking the person's
withdrawal reflex, thus causing the leg LG to move and thus initiate
swing phase. Such stimulation S of course requires an intensity to
trigger the withdrawal reflex, and typically the required intensity is
perceived as less pleasant. The stimulator STM is controlled in response
to a control signal CS generated by a processor unit PU which runs a
control algorithm CA. This control algorithm CA calculated the control
signal CS in response to a feedback signal FB which the processor unit PU
receives from a sensor SN which is arranged to sense a parameter, e.g.
acceleration of the leg LG, here illustrated as a goniometer sensing the
knee angle, and generates the feedback signal FB according to this
parameter. The control algorithm CA is preferably designed to adjust the
control signal CS so as to obtain a target trajectory for the leg LG. In
the illustrated example, the control algorithm CA may be designed to
determine a control signal CS resulting in a stimulation S that would
most probably provide a target knee angle of the leg LG as a function of
time during one walking step.

[0035] The sensor SN may in addition to or as an alternative to a
goniometer include a simple contact or switch mounted to sense if the
foot FT touches the ground, thus providing valuable position for the
control algorithm CA with respect to determining when a gait cycle is
initiated. It is to be understood that several sensor types may be used
to derive a feedback signal which represents a parameter describing the
position and/or movement of the leg during the gait. This could be
accelerometers, tiltsensors and gyroscopes that are used for estimating
the position of the leg and thereby joint angles. E.g. a camera can be
used to capture digital images of the leg during the patient walking. Via
appropriate image analysis processing on the image, a suitable feedback
can be derived, e.g. in the form of one or more of hip, knee, and ankle
joint angles and foot distance to ground, or in the form of a more
complex parametric description of the leg movement.

[0036] Preferably, the stimulation S is an electric stimulation which has
the form of electric current bursts of 5 pulses with a duration of 1 ms,
with inter-stimulus intervals of 4 ms. Sequences of 4 such bursts have
been found to be optimal, however it is to be understood that all of
these stimulation parameters may be varied in order to obtain an optimum
gait quality, taking into account reflex habituation effects. The
electrode impedance is known to vary significantly over time, and thus it
is preferred that electric stimulations with a constant current are used.
This helps to provide a stimulation S which is independent on the actual
electrode impedance and thus controllable. However, it is preferred that
the amplitude of the stimulation S can be varied on purpose so as to
adapt the stimulation S intensity to the sensed feedback.

[0037]FIG. 2 also shows a sketch of a therapy device embodiment. This
embodiment differs from the one in FIG. 1 in that the stimulator STM
includes a plurality, here four, separate stimulator channels and
associated electrodes. The stimulator channels are spatially distributed
so as to be able to apply four separate stimulations S1-S4 at different
positions on the foot FT. As illustrated, one stimulation position is on
the posterior heel, while the remaining three positions are different
position on the sole of the foot, spatially distributed in a length
direction of the foot FT. Especially, the heel position can be used to
initiate a forward swing of the leg LG, while a distal part of the sole
of the foot can be used to cause a dorsi flexion of the foot FT ensuring
ground clearance during the swing phase. Hereby, the control algorithm CA
can be designed such that an optimal gait can be obtained by
appropriately determining a control signal CS that selects to stimulate
the foot FT appropriately by one or more of the stimulations S1-S4, and
especially the stimulations S1-S4 should be applied at the most optimal
time during the step cycle. To do so, the control algorithm CA may be
arranged to select between a fixed number of different predefined
stimulation scenarios, e.g. by calculating for each predefined scenarios
an estimated mean square error from a target trajectory, and thus
selecting the scenario with the lowest mean square deviation.

[0038] The plurality of stimulations S1-S4 at different positions can be
used to reduce habituation effects, i.e. reduce the effect that several
stimulations at one position causes a reduced reflex response, or no
reflex response at all. Especially, it has been found that the
habituation can be "reset" by one high intensity stimulation at another
position or site on the foot FT, thus causing the reflex response to
return to normal. Such monitoring for habituation by monitoring the
feedback signal FB and appropriate shift in stimulation position is
preferably implemented in the control algorithm CA.

[0039]FIG. 3 illustrates a basic principle which is utilized in aspects
of the invention, namely the provoked stimulation of the NWR, i.e. the
spinal cord reflex pathway which causes activation of multiple muscles in
a person's leg to withdraw the leg in response to a painful stimulation.
This reflex is possible to provoke in a person suffering from a stroke,
and thus cause a leg movement which can be used in gait training, even
though the person is unable to move the leg voluntarily due to damage to
supraspinal motor pathways. The muscle control, which is still
functioning in the spinal cord is utilized to activate leg muscles. Early
gait training is a vital part of therapy after a stroke, as full or
partial recovery of gait function is most efficiently obtained by early
applying the brain with appropriate sensory feedback during persistent
gait training. This early gait training thus enables the brain to
automatically spatially rearrange the motor control associated with
walking and thus restore the ability of walking.

[0040] Even though the reflex may be considered to be a stereotyped
reflex, it has been found that the human lower limb nociceptive
withdrawal reflex elicited by painful electrical stimulation of the sole
of the foot depends strongly on the stimulation site. If stimulation is
applied to the forefoot this will primarily evoke ankle dorsiflexion
through tibialis anterior activation. If the stimulation is applied to
the heel, it primarily evokes ankle plantar flexion via soleus
activition. Activation of hip flexors can be achieved for any stimulation
site on the sole of the foot and is substantially modulated during the
gait cycle. This is preferably utilized in gait therapy, which therefore
preferably includes a plurality of stimulation positions.

[0041]FIG. 4 illustrates four basic phases of a gait cycle and the use of
four different stimulation positions on the foot to be used at different
periods during the gait cycle. To initiate a leg swing, at least
stimulation on the heel is preferred, but more foot sole positions may be
used in addition or alternatively to ensure ground clearance during the
swing phase. When the forefoot hits the ground, stimulation of the
frontal part of the foot sole may be initiated in order to cause an
upward flexing of the foot. Typically it is not possible to obtain such
upward flexing of the foot in response to a sensor signal, i.e. with
close-loop feedback, since the delay in the reflex is too large. However,
it is possible to simulate different positions or times during a walking
step where such upward bending of the foot can be utilized and thus
stimulation of this reflex may form part of the total stimulation during
a walking step.

[0042] FIGS. 5-7 sketch different therapy device implementations suitable
for rehabilitation of a patient since the embodiments allow easy mounting
and easy removing. Thus, the embodiments are suited for normal therapy
situations with a rather limited total time available for therapy of each
patient. The simple mounting thus allow high utilization for the actual
gait training of the patient with a limited waste of time spent on the
therapy equipment.

[0043] FIG. 5 illustrates an embodiment where the sensor system includes
separate hip, knee, and ankle goniometers and a foot switch to sense when
the foot is in contact with the ground. Separate switches may be used to
sense when the fore foot and heel are in contact with the ground, thus
enabling sensing both when the foot touches the ground, and when the foot
leaves the ground. Preferably, the sensor placed on the person's ankle
includes an accelerometer and/or gyroscope the sense additional
parameters related to the movement of the person's leg during a walking
step.

[0044] The stimulator can be an electric stimulator with less than or
equal to about 4 stimulation electrodes: e.g., one electrode to stimulate
the posterior heel, and 3 electrodes to stimulate three different
positions on the sole of the foot. The processor unit is implemented with
a computer, e.g. a notebook PC, which is connected to an input interface
unit serving to interface the sensors. Further, the computer is connected
to the stimulator in the form of an output interface which generates the
electric signals to the electrodes. The control algorithm is implemented
in software which is executed on the computer.

[0045]FIG. 6 illustrates an embodiment with the same sensors and
stimulators as the embodiment of FIG. 5, however here a portable device
in the form of a battery driven device placed on the belt includes
hardware to interface the sensors and to generate the electric signals to
the stimulators. The belt device communicates with a computer, e.g. a
notebook PC, via a wireless link. The control algorithm is then run on
the computer, as already described for FIG. 5. The belt device thus
communicates the feedback signal via the wireless link to the computer
and receives in response a control signal which it translates into
electric signal(s) which is applied to the appropriate one(s) of the
electrodes.

[0046]FIG. 7 illustrates yet another embodiment which in its basic
structure is similar to the one shown in FIG. 6. However, as illustrated,
the sensor is here implemented as a gait detection unit which, e.g. by
means of one or more accelerometers and/or gyroscopes, tiltsensors, that
generates a feedback signal which is wirelessly transmitted to the belt
device or directly to the computer. The belt device is connected to the
stimulation electrodes by means of a cable which is attached to the
patient's leg by means of a Velctro® strap. Such Velctro® strap is
also used to attach the gait detection unit to the lower leg of the
patient. Alternatively, the gait detection unit may be attached to the
patient's shoe. The stimulation electrodes are seen to be placed in an
insole suited to fit into the patient's own shoe or into a dedicated
training shoe. The electrodes are placed in the upper surface of the
insole so as to allow direct contact with the skin on the foot sole and
heel of the patient. Preferably, the insole is adhesive to the sole of
the foot so as to ensure proper electrode contact.

[0047] It is to be understood that in all the illustrated embodiments,
goniometers may be entirely replaced by sensor(s) in the form of
accelerometer(s) and/or gyroscope(s). Especially, it may be preferred to
build in such accelerometer(s) into a part of an in-sole.

[0048]FIG. 8 shows in schematic form an implementation of a control
algorithm which can be regarded as a modified Model Reference Adaptive
Control system (MRAC). Conventional MRAC concepts are associated with
parametric models, but in this application neither model structure nor
parameter values are known. Instead, a novel modified MRAC method is
introduced, in which models of entire kinematic trajectories (Y) in the
heel-off phase are recursively derived from input-output data for three
joint angles (hip, knee, and ankle) obtained from physical sensors or
estimated from alternative sensor signals. Such alternative sensor signal
may be input from one or more or a gyroscope, a accelerometer, or a tilt
sensor which is used to calculate a position of the leg, e.g. in the form
or one or more a joint angles based on these sensor inputs. Based on the
kinematic trajectory model, the controller continuously compares the
deviation of the present step to a target trajectory. The controller
minimizes the error e2 between the predicted output and the target
trajectory. Changes in the baseline gait pattern or in the reflex
response induces changes in a plant model implicitly embedded in the MRAC
controller. The controller then predicts all outcome possibilities and
chose the combination of Intensity, Duration, Site and Phase that results
in the lowest error; the embedded plant model forces thereby the adaptive
controller to change the stimulation parameters, if needed.

[0049] The MRAC strategy includes: specification of a reference model with
the desired dynamics and on-line parameter estimation. The system
comprises an ordinary feedback loop composed of process and controller.
The error (e2) is the squared difference between the predicted
outputs of the system (Y) and the reference model (Ym). There are
two loops in the system: an inner loop, which provided the ordinary
control feedback and an outer loop, which adjusts the parameters in the
inner loop. Thus, the aim for the closed-loop system is to follow the
reference model trajectory Ym, while the neuro-muscular plant model
is described by .

[0050] The use of trajectories, rather than parameterized dynamical
input-output models, is stressed by the use of the symbol for the
individual coordinates.

[0051] The dynamics of the outer loop, which adjusted the controller
parameters, is normally assumed to be slower than the inner loop and the
adjustments are often based on a gradient approach. However, since a
parametric model is not available for the present system, the gradient
approach is deemed infeasible. It is crucial to reflect gait improvement,
habituation, and fatigue as well as to reduce noise from normal
step-to-step variability. This is achieved by introducing a simple moving
average (MA) approach for modeling the kinematic reflex responses
trajectory, where the length of the MA-filter reflects the adaptation
rate.

[0052] The predicted trajectory, , is considered to be a sum of two
parts: a contribution from the kinematic reflex responses, MA, and
a contribution from the unperturbed gait (baseline trajectory, B).
This results in a step trajectory Y(t).

[0053] In a concrete implementation example, both models (Y .sub.∥MA
rY .sub.∥B) may be continuously updated. By disabling the
stimulation with a five step interval, a baseline-step may be acquired
and used as an updated B, by letting B=Y . In the other four
controller-corrected-steps, the reflex response model ( MA) is
updated by first calculating the reflex response as the error between the
present step and the latest baseline-step (e1=Y- B) and then
use a simple MA approach for estimating MA at time t. The MA of the
last five steps corresponding to the same input parameters can then be
calculated.

[0054] At the end of each swing phase, immediately after the update of the
adaptive neuro-muscular plant model, the controller algorithm calculates
the predicted step ( ) for all combinations of stimulation site and phase
based on the adaptive neuro-muscular plant model.

[0055] Additional features that may be present in one or more of the
embodiments described herein, in particular regarding the implementation
of the control algorithm may be found in any one or more of the following
references, all of which are hereby expressly incorporated by reference
in their entireties: [0056] Ph.D. thesis: "Modulation of the nociceptive
withdrawal reflex and its use in rehabilitation of gait of stroke
patients", J. Emborg, Center for Sensory-Motor Interaction (SMI),
Department of Health Science and Technology, Aalborg University, 2009
[0057] "Withdrawal reflex responses evoked by repetitive painful
stimulation delivered on the sole of the foot during late stance: site,
phase, and frequency modulation", E. G. Spaich, J. Emborg, T. Collet, L.
Arendt-Nielsen, and O. K. Andersen, Exp. Brain Res., vol. 194, no. 3, pp.
359-368, April 2009 [0058] "Withdrawal reflexes examined during human
gait by ground reaction forces: site and gait phase dependency", J.
Emborg, E. G. Spaich, and O. K. Andersen, Med. Biol. Eng. Comput. 2009;
vol. 4, pp. 29-39, January 2009 [0059] "Novel method exploiting the
nociceptive withdrawal reflexes in rehabilitation of hemiplegic gait"
Emborg, J.; Bendtsen, J. D.; Spaich, E. G.; Andersen, O. K., 2009. s.
84-87 World Congress on Medical Physics and Biomedical Engineering,
Munich, Germany, 7-12 Sep. 2009, International Federation for Medical and
Biological Engineering Proceedings. 25. IX

[0060] Accordingly, embodiments described herein provide a device and
method for gait training, such as for rehabilitation of a person after a
stroke. The devices comprise a stimulator, preferably electric
stimulator, for provoking a spinal cord withdrawal reflex in a person
(also referred to as a "subject" in some contexts though it should be
understood that the term subject also encompasses mammals as a class
including, but not limited to, humans) by stimulation of the person's or
subject's foot in response to a control signal. Hereby, the person's leg
will move and initiate a gait swing. A sensor is placed to sense movement
of the leg and provide a feedback signal accordingly. A processor unit
with a processor runs a control algorithm which calculates the control
signal in response to the feedback signal. Thus, the method is based on a
closed-loop design, and the control signal is preferably calculated for
each walking step, and it is preferably based on the feedback signal
obtained from the preceding walking step. Hereby reflex habituation can
be accounted for. Preferably, the stimulator has a plurality of
stimulator channels with electrodes placed on different sites distributed
on the sole of the foot and on the heel. The feedback signal may be based
on accelerometer(s), and/or gyroscope(s), and/or goinometer(s) positioned
on the leg and/or foot, e.g. partly or fully integrated in an in-sole for
a shoe etc.

[0061] Although the present invention has been described in connection
with preferred embodiments, it is not intended to be limited to the
specific form set forth herein. Rather, the scope of the present
invention is limited only by the accompanying claims.

[0062] In this section, certain specific details of the disclosed
embodiments are set forth for purposes of explanation rather than
limitation, so as to provide a clear and thorough understanding of the
present invention. However, it should be understood readily by those
skilled in this art, that the present invention may be practised in other
embodiments which do not conform exactly to the details set forth herein,
without departing significantly from the spirit and scope of this
disclosure. Further, in this context, and for the purposes of brevity and
clarity, detailed descriptions of well-known device, circuits and
methodology have been omitted so as to avoid unnecessary detail and
possible confusion.

[0063] In the claims, the term "comprising" does not exclude the presence
of other elements or steps. Additionally, although individual features
may be included in different claims, these may possibly be advantageously
combined, and the inclusion in different claims does not imply that a
combination of features is not feasible and/or advantageous. In addition,
singular references do not exclude a plurality. Thus, references to "a",
"an", "first", "second" etc. do not preclude a plurality. Reference signs
are included in the claims however the inclusion of the reference signs
is only for clarity reasons and should not be construed as limiting the
scope of the claims.